Many mechanical operations are carried out downhole in connection with establishing, maintaining and optimizing production from oil and gas wells. Many of these operations require the tool to be held fixed in the well by anchoring in a specific place by means of anchoring devices.
Prior art in the field includes anchor systems with hydraulic pistons that are pressed against the pipe wall. It is then known to use one or more such hydraulic pistons, wherein these are distributed in the circumference of a well tool. Solutions in which hydraulic pistons cooperate with anchor systems based on the toggle-joint principle, in which an anchor foot has a link arm at either end, are known as well. One link arm is attached to the well tool and the other to a hydraulic piston. There may typically be three anchor feet connected to the same hydraulic piston. When the anchor is inactive, it lies flush with the body of the well tool. The anchor is activated by the hydraulic piston being pressurized so that the link arms are driven towards each other and the anchor feet move outwards into contact with the pipe wall. Such anchor systems are sensitive to diametrical changes in the pipe. It is also known to use a cone which drives wedges out against the pipe wall. Common to the prior-art solutions is that they hold the well tool fixed in a centred position so that the well tool is concentric with the well.
In those cases in which the well tool is to carry out operations in a radial direction, such as when perforating a pipe, the radial reach of the tool is limited. This is a challenge when a petroleum well has been drilled and is to be prepared for production, among other things. In this so-called completion phase, the well will be provided with casing which, in turn, is perforated in the areas assumed to give the best production. Perforation is also relevant in other phases of the production, in injection wells and by well intervention. Further, perforation may be performed in open wells, that is to say with no casing, to increase the extraction from a zone.
According to the prior art, a perforation tool is lowered down to the desired area in the well and the perforation tool is used to make the necessary number of holes in the casing. The perforation tool usually includes a row of small explosive charges which are detonated at the desired place. The use of explosives may give an uneven hole quality and sometimes no hole at all. The handling and transport of explosives are becoming increasingly difficult because of stricter legislation. An alternative to using explosives, which is prior art as well, is punching holes by means of hydraulic pressure. However, this is only an alternative in pipes with thin walls. Punching requires much, heavy and space-demanding equipment. It is always a challenge to have enough room for equipment in well tools which are generally of small diameters.
Radial drilling may also be used to perforate pipes. A known well tool used for this is the applicant's own tool called “MaxPERF” developed by the Canadian company Penetrators Canada Inc. Said tool drills holes with a diameter of 1″ (≈25.4 mm) in casings and longer tunnels or bores with a diameter of 0.7″ (≈17.8 mm) in the formation outside. These two drillings, through the casing and into the formation, respectively, are performed with two different applications accommodated in the same tool. Drilling through casing requires a steady and stable drilling device, whereas the longer tunnels can be drilled with a flexible string-shaped drill.
When perforating by means of drilling, unintentional damage to the casing and/or formation outside is avoided. By drilling, the diameter of the hole will be known and, in addition, drilling gives considerably greater control of the depth of the hole and drill-through can be verified. In connection with injection wells, injection calculations will thus be more accurate as well. With the limited diameter that a well tool has got, one of the challenges connected to drilling as the perforation method is to get a sufficient length of stroke for the drill so that even thick casings can be perforated.